The German patent DE 37 10 489 C2 discloses a plasma coagulation apparatus intended for use in open surgery. In this apparatus argon is ejected from a nozzle in the center of which is a discharge electrode, with sufficient pressure and flow velocity that in addition to the coagulation effect produced by an arc formed between the electrode and the tissue to be coagulated, fluids "floating" on the tissue are pushed away. With this arrangement the risk of embolism is very high. Furthermore, it is extremely problematic to use this apparatus in body cavities because the large amounts of gas typically introduced in the cavities can lead to undesired insufflation effects.
A coagulation apparatus for use in an endoscope is known from U.S. Pat. No. 5,207,675. In this apparatus a tube, within which an electrode is slidably disposed, is inserted into the working channel of an endoscope in such a way that it can be manipulated within said channel by means of a handle, like an (ordinary) instrument. The electrode, which should simultaneously be constructed as an instrument, is kept in a state such that it projects from the tube when in the working (coagulating) mode, in which argon is expelled from the tube that houses the electrode. While in this state, if the electrode touches the tissue to be coagulated, considerable tissue damage can result. In the case of thin-walled tissues, the consequences (rupture, etc.) can be fatal.
In DE 195 35 811 A1 a coagulation apparatus of the kind cited above is described that goes some way toward avoiding the substantial problems associated with the arrangements just described. In particular, the end of the tube housing the electrode is so constructed that there is no danger of embolism even when a relatively strong gas stream is applied, during which time the electrode is withdrawn into the gas-emitting tube far enough that it cannot make direct contact with the tissue. However, this arrangement is relatively complicated to manufacture.
The object of the invention is to disclose a coagulation apparatus that ensures increased safety in use and improved operation, while reducing the manufacturing complexity and cost.